WO2020081022A1

WO2020081022A1 - Detector capable of showing the underground cavities

Info

Publication number: WO2020081022A1
Application number: PCT/TR2018/050613
Authority: WO
Inventors: Mehmet ONLEK
Original assignee: Nokta Muhendislik Ins. Elekt. Plas. Gida Ve Reklam San. Tic. Ltd. Sti.
Priority date: 2018-10-19
Filing date: 2018-10-19
Publication date: 2020-04-23

Abstract

The present invention is a metal detector or magnetic detector (10) visualizing for the user, the underground (1) irregularities and cavities (2) and it is characterized by containing; a detector (10) of which the operation frequency, search head (11) geometry and signal processing system are optimized for detection of the ground (1) properties and which provide the reception of the signals related to the ground (1) properties; a position tracking unit (20) integrated into the detector (10) structure in a manner to track the ground (1) scanned by the search head (11) of the mentioned detector (10) by optical flow method, which provides the position data on the ground (1) scanned by utilizing the movement of the shades, in other words the patterns created by the geometric irregularities on the ground (1), in the image frame; at least one internal and/or external graphic processing unit (30) which provides the signals concerning the content of the ground (1) received from the detector (10) and position data received from the position tracking unit (20) simultaneously with the mentioned signals, to be converted into at least three dimensional series or matrix and defines the mentioned series or matrix as isometric curves and color visuals and accordingly, displays these on an internal and/or external display (32) by visualizing and/or mapping.

Description

DETECTOR CAPABLE OF SHOWING THE UNDERGROUND CAVITIES Technical Field

The present invention relates to a device and its operation method which visualizes the shape of the underground cavities and the irregularities of such cavities on any display by means of an optical flow based position measuring unit and graphic signal processing unit connected to a hand-held detector optimized to detect the ground properties. Prior Art

An underground cavity can be the foundation of an old house, an old tunnel, a pit, an archeological grave and similar structures. The targets where the ancient habitants co-exist in a larger cavity and usually at the lower parts of such cavities. Due to this; the determination of the cavities is as important as detection of the target (object) for the detectors. This criterion enables the decisions to be given for the digging to be carried out.

The systems aiming the target directly (known metal detectors etc.) operate under a principle which only provides direct detection of the target. On the other hand, a cavity detector detects the cavities under the ground, where the probability to find a target (object) is high and enables the detection of the targets which are out of range. In the state of the art, there are some methods used to detect the cavities under the ground (or behind an obstacle) or the irregularities of the underground. In the state of the art, some metal detector and magnetic detector (gradiometer) based devices used together with the additional apparatus and methods can detect the presence of the underground cavities to some extent. However, the detection of the cavity only is not sufficient for determining the type and borders of such cavity. In order to detect the type and borders of the cavity, it is required to determine at least the horizontal geometry of the cavity in question. For determination of the borders and types of the underground cavities, it shall be possible to make comments concerning such cavity if the visual expression of the data related to such cavity is enabled. The devices used in the state of the art, in order to form the mentioned visuals, require the search head of the magnetic detector or metal detector to be moved in an orderly manner for scanning. Moreover, while moving for scanning, it is required to pay attention to a stable speed and alignment and repetitions are required to be performed. In the mentioned method; the detector search head cannot be used by the user with his natural search swings. Also, this scanning method may result in critical errors specifically in integration of the image due to the user’s hand and body movements. The errors related to the shape of the cavity obtained with the existing method increases with the size of the cavity. In this case, the cavity image obtained with the mentioned method is usually misleading.

In the state of the art, the devices measuring the geological conductivity by electrical current (Electrical Resistivity Tomography) can detect the differences in the soil conductivity and accordingly, these can be used for finding the cavities. However, these devices provide detection concerning the presence of a cavity by the electrodes that are nailed to the ground. It is not possible to obtain any detailed information practically with respect to the horizontal position geometry of the cavity with the mentioned devices.

The patent document with publication US 5629626 A dated 1994 mentions a device and method in order to find the irregularities by tracking the position of the detector with the help of GPS. The mentioned device and method can be used especially on a large scale area. In the document the type of the device which can be by a vehicle or trailer is mentioned and the type that can be carried by the user (man) is also described. However, the mentioned device is designed for the macro- size processes that unite the information about the cavities, on a map, not the details of a cavity detected. The use of GPS does not enable the analysis of the area belonging to the cavity, below a meter. In that document, although a“micro-navigation system” concept is mentioned, a sensor tracking the position of the detector in centimeters is not mentioned. Within this context, the mentioned accelerometer, inclinometer and the sensors such as height sensors are directed to the positional problems within the magnetic sensor (horizontality, axial movements etc.) which is the main data source.

GPR (Ground Penetrating Radar) devices used in the state of the art, can display layers based on permeability, via radar technique. The mentioned display is usually realized on the vertical direction and it usually tracks a single line. Moreover, the performances of GPRs vary as based on the type of ground and the physical parameters (humidity, wetness, temperature etc.) of the ground. GPR devices are required to be operated as close to the ground due to the structure of their antennas and they are appropriate only for flat grounds.

The patent document with publication no US8510048B2 in the state of the art mentions a method which aims to find the tunnel structures with a gravitational analysis, by measuring gravitational gradients. Since there is no position measuring mechanism in the mentioned device, the data collected by passing it over the ground at a stable speed (like gravitation measuring from an airplane as mentioned in the document) is analyzed. The accelerometer mentioned in the document is defined for measuring the gravitation. In the mentioned device and the method, there is no function equivalent to IMU in order to correct the optical flow and similar process.

Optical flow has its application area in the state of the art. This subject was first used as a term related to the visual perceptions of the animals, in l940s by the American psychologist James J. Gibson. In the state of the art, the position tracking by optical flow is frequently used in the pointing tools used in the computers, and specifically as an optical mouse. Optical flow sensors are required to be integrated with the other sensors so that more sensitive position tracking sensitive to the movements on the different axis with optical flow is possible. These integration applications are used in various areas in the state of the art. For example; the use of optical flow for the actual position marking process is mentioned in the patent application no US20130002854A1 with the title“Marking methods, apparatus and systems including optical flow-based dead reckoning features”. In the mentioned device, various sensors (like IMU) are integrated in order to assist the position tracking.

The device mentioned in the patent document no US9841503B2 with the title“Optical ground tracking apparatus, systems, and methods” which is about the integration of the sensors, contains a magnetic detector and an optical ground tracking unit connected to this detector. However, the mentioned device does not offer any solution for finding the cavities and for perception of the shape of such cavities. The mentioned device aims finding and tracking certain types of targets (cables, pipelines). In the state of the art, there are some documents about the methods for detection of underground cavities:

In the document no CN104459763 A with the title“Method and system for detecting position of underground cavity through compactly supported wavelet”, a method operating with the seismic data (Rayleigh waves) and used for detecting whether there is a cavity at a location is described. In the mentioned method, no solution is offered for detecting the shape of the cavity.

In the document no CN102662195B with the title“Underground cavity detection system”, especially detection of the geographical cavities under the roads with GPR (Ground Penetrating Radar) technique is described. In the mentioned document, the integration of GPR technique with GPS data is mentioned. GPS data may be appropriate for the cavities of the size mentioned in the document and for a large area. However, GPS resolution is not sufficient for the display of the cavities opened by men with relatively smaller dimensions. A method operating at centimeter scale is required in order to display the details concerning the cavities with relatively smaller dimensions and irregularities.

In the patent document no KR100831932 with the title“3-D gravity inversion method of underground cavities using Euler deconvolution and 3-D imaging method using it”, a geodesy and geophysics method known as“gravity inversion”, which is used to measure the depth of the underground cavity, is mentioned. Visualization of the large cavities in the underground layers for geodesic purposes (caves, air gaps, water layers etc.) and accordingly underground mapping is aimed with the mentioned method. The mentioned method aims the visual display of large dimension cavities by analyzing the data collected during a long process. In the mentioned method, there is no solution offered for the visualization of the relatively small size cavities (opened by men) with relatively short time and random measurements.

Short Description of the Invention

The present invention relates to a device and the operation method of the mentioned device for finding the cavities and for displaying the shape of such cavities on an internal and/or external display, by an optical flow position tracking unit integrated into a metal detector of magnetic detector optimized in order to detect the ground properties. The present invention enables the detection of the cavities with higher probabilities of having underground targets. Accordingly, the targets below the detection depth of a detector operating for the target can be detected by interpretation of the underground cavity and irregularity visuals. Moreover, it is not required for the targets that may be present in the cavities to have a specific physical property (like being metal) since the cavities with higher probabilities of containing targets, not the direct targets, are detected with the detector capable of showing the underground cavities.

Since any abnormal underground formation with regular borders (irregularity) can mean pits, graves, house foundations etc. made by men, it is very important to know the shape of the cavity. The present invention enables the visualization of the underground cavities with a hand-held detector optimized to detect the ground properties; an optical flow position tracking unit integrated into the mentioned detector; various secondary sensors (IMU, height sensor etc.) enabling the mentioned position tracking without being influenced by the movements of the detector at different axis (due to the user’s intentional or unintentional body and hand movements etc.) and the surface changes in the ground

(heights, holes etc.) and an internal or external graphic processing unit.

Description of the Invention

The present invention relates to a device and method providing the horizontal projection of the visuals related to the underground cavities by integration of the position data obtained from the position tracking unit operating under optical flow method with the signals concerning the ground given by the detector optimized in order to detect the ground properties

The metal detector or magnetic detector (magnetic gradient detector) optimized in order to detect the ground properties can be used for receiving the signals related to the composition of the ground scanned. The metal detector shall be mentioned with respect to the preferred embodiment of the invention.

The signals related to the ground conductivity and the ferromagnetic response received by the metal detector or the magnetic detector from the ground scanned; are combined with the position information created by a position tracking unit connected to the detector body. Combined data is shown visually to the user on an internal or external display, in the mapping form by the signal and graphic processing methods. Graphic processing unit can be an internal unit within the detector or can be an external unit. The position tracking unit integrated to the detector displaying the underground cavities basically operates with the optical flow method. The position tracking unit performs instantaneous position detection simultaneously with the signals acquired by the detector. The accomplishment of the mentioned position detection with minimum errors, without limiting the free movements of the user (and accordingly, the detector) and without being influenced by the changes in the ground surface is achieved by the various sensors integrated into the position tracking unit. The position tracking unit contains an accelerometer and gyroscope and/or an integrated IMU sensor measuring the axial movements because of the user’s hand and body movements. The distance of the optical flow sensor to the ground can be measured by a non-contact distance measuring sensor. Accordingly, the axial movements of the device are detected and the ground surface roughness are taken into account while integrating the underground signals with the position data.

The detector displaying the underground cavities has a graphic processing unit which collects, processes and visualizes such data. The mentioned graphic processing unit can be within the detector structure whereas it can also be within the structure of an external computer or processor where the signals and data received from the detector are collected.

The present invention is explained in more detail, referenced by the figures and graphics listed below:

Description of the Figures Figure 1: The perspective view of a preferred construction of the detector displaying the underground cavities.

Figure 2: The side view of a preferred construction of the detector displaying the underground cavities. Figure 3: The detailed view of the position tracking unit of the detector displaying underground cavities.

Figure 4: The view of the signal graphic of the detector displaying underground cavities based on its operation form and position on the ground.

Figure 5: The top view of the operation method over the ground of the detector displaying underground cavities.

Legend

NO NAME OF THE PART

1 Ground

2 Cavity

10 Detector

11 Search head

12 Shaft

20 Position tracking unit

21 Optical flow camera

22 Optical flow processor

23 Distance measuring sensor

24 Gyroscope

25 Accelerometer

26 Lighting element

27 Cold mirror filter

28 Lens 30 Graphic processing unit

31 External graphic processing unit

32 Display

40 Wireless antenna

Detailed Description of the Invention

The detector(lO) displaying the underground(l) cavities(2) basically contains; a detector(lO) detecting the properties of the ground(l) and producing the signals for such ground(l); an integrated position tracking unit(20) integrated on the detector(lO) obtaining the position data by optical flow method; a graphic processing unit(30) processing and visualizing the signals related to the ground(l) properties provided by the detector(lO) and the position data obtained from the position tracking unit(20).

The present invention is a metal detector or magnetic detector(lO) visualizing for the user, the underground(l) irregularities and cavities(2) and it is characterized by containing; - A detector(lO) of which the operation frequency, search head(l l) geometry and signal processing system are optimized for detection of the ground(l) properties and which provide the reception of the signals related to the ground(l) properties;

A position tracking unit(20) integrated into the detector(lO) structure in a manner to track the ground(l) surface scanned by the search head(l l) of the mentioned detector/lO) by optical flow method, which provides the position data on the ground/ 1) scanned by utilizing the movement of the shades, in other words the patterns created by the geometric irregularities on the ground/ 1), in the image frame, or the sub-elements integrated into the detector/lO) body separately or in groups which perform the mentioned position tracking;

At least one internal and/or external graphic processing unit(30) which provides the signals concerning the content of the ground/ 1) received from the detector/ 10) and position data received from the position tracking unit(20) to be converted into at least three dimensional signal-position data series or matrix and defines the mentioned series or matrix as isometric curves and/or color visuals and accordingly, displays these on an internal and/or external display(32) by visualizing and/or mapping;

An optical flow camera(2l) and processor or integrated optical flow sensor within the position tracking unit(20), which provides the detection of the movement of the ground/ 1) patterns by optical flow;

At least one no-contact distance measuring sensor(23) within the position tracking unit(20), which provides the continuous measuring of the distance of the optical flow camera(21) to the ground(l);

At least one IMU sensor, within the position tracking unit(20) containing at least one gyroscope(24) and at least one accelerometer(25), which provides the detection of the axial movements of the detector/ 10) originating from the user’s hand and body movements during the scan.

A preferred model and a basic operation method of the invention are as given below:

In the embodiments of the invention metal detector or magnetic detector can be used as the detector/ 10). The detector/ 10) mentioned in the invention is optimized in order to detect the properties of the ground/ 1). The detector/ 10) detects the cavity(2) under the ground/ 1) by utilizing the changes (contrarieties, irregularities etc.) occurring in the continuity of the signal created by the content of the ground/ 1) and from the decrease of the signal. The mentioned ground/ 1) present conductive and/or ferromagnetic characteristics. The metal detectors can measure the conductivity and ferromagnetic characteristics of a target or medium, together. On the other hand, the magnetic detectors measure only the ferromagnetic characteristics.

Although the detector/ 10) can be either a metal detector or a magnetic detector in principle; it can measure the conductivity and/or the ferromagnetic characteristics of the ground/ 1 A typical metal detector/ 1) is optimized in order to eliminate the ground/ 1) effects, not to specifically measure them. In the detector(lO) of the invention, the operation frequency, search head/ 11) (bobbin) geometry and signal processing system are optimized in a manner to detect the properties of the ground(l). The metal detector/ 10) preferred in the invention is designed as a device in which the measures such as signal filtering, ground balancing and similar functionalities are changed intentionally in a manner to detect the characteristics of the ground(l) (soil).

The detector(lO) displaying the cavities(2) under the ground(l) has an integrated position tracking unit(20) which obtains the position data. Optical flow method is used for tracking the position of the device in the present invention. The relative movement of the shades, in other words the patterns, consisting of geometric irregularities above the ground(l), in the image frame is used for position tracking by the optical flow method. Integrated position tracking unit(20) is consisting of the optical flow camera(21), optical flow processor(22) and the auxiliary sensors (IMU, accelerometer(25), gyroscope(24), distance measuring sensor(23) etc.). The position tracking unit(20) is fixed on the detector(lO) body or the search head(l l) in a manner to move together with the detector(lO) search head(l l). In a preferred embodiment of the invention, the position tracking unit(20) is mounted on the detector(lO) shaft(l2).

The optical flow camera(21) within the position tracking unit(20) can either consist of an integrated image sensor modified for optical flow or a camera directly showing the ground whose images are processed by a DSP (“Digital Signal Processor”). In the preferred embodiment, an integrated image sensor with optical flow capability has been used.

The ground(l) scanned by the detector(lO) is sensed by the optical flow camera(21) and the movement of the patterns on this image is processed by the optical flow processor(22). The movement in the image depends on the height of the optical flow camera(2l) from the ground(l). Due to this reason, non-contact distance measuring sensor(23), which provides the continuous measuring of the height of the optical flow camera(21) above the ground(l), is used in order to determine the actual amount of change in the position. Non-contact distance measuring sensor(23) operates by measuring the ToF (Time of Flight) of light, sound and similar wave. The mentioned measuring can also be realized by stereoscopic, geometric methods or any method using projection or any similar technique. In the preferred embodiment of the invention, an infrared non-contact distance measuring sensor is used. The position tracking unit(20) may contain lighting elements(26) and preferably cold mirror filter(27) to illuminate the ground so that the optical flow camera(2l) receives sufficient light. For energy saving purposes, the light intensity of the lighting elements(26) can be adjusted as based on the system requirements. Moreover, the lens(28) of the optical flow camera(21) can have a moving structure.

The detector(lO) described in the present invention is a hand-held device which is used by free movements. The use of the detector(lO) with free movements resultantly causes the height of the search head(l l) and the position tracking unit(20) from the ground(l) to change persistently and be subject to axial movements. Despite the user movements and the changes in the ground(l) height, the detector(lO) has the capability of obtaining the actual values during the optical flow via the auxiliary sensors. Within the structure of the mentioned detector(lO), there is at least one non-contact distance measuring sensor(23) which continuously measures the distance with the ground(l) and at least one IMU sensor in order to detect and correct the axial movements of the search head. There is at least one gyroscope(24) and at least one accelerometer(25) in the IMU sensor which collects the angular speed and linear acceleration data in a single module.

An integrated structure which is formed by a gyroscope(24) or MEMS (Micro Electro- Mechanical Systems) solutions having the same function with the gyroscope(24) in the IMU sensor for measuring inertia is used. Moreover, there is an integrated structure which is formed by an accelerometer(25) or MEMS solutions having the same function with the accelerator(25) in the IMU sensor for measuring the acceleration.

The data obtained simultaneously from the detector(lO) composing the ground(l) content signals and data from position tracking unit(20) are combined as a series or matrix forming the signal information related to the position (the continuity, presence absence, intensity, level of the signal etc.) in the graphic processing unit(30). The graphic processing unit(30) can be integrated into the detector(lO), whereas it may also be a mobile unit, laptop, smart phone, tablet or a similar external graphic processing unit(3l) apart from the detector(lO) structure, which receives the data with cable or as wireless. A preferred embodiment of the invention is structured as an external graphic processing unit(3l) carried as detached from the detector(lO), capable of receiving the data (information) about the ground content and the position from the detector(lO) through its wireless communication units(40), which presents to the user, the visuals related to the ground(l) and cavity(2) via display(32) on it.

A possible embodiment of the invention is as follows:

The user performs the scanning by moving the detector(lO) and the search head(l l) freely above the ground(l). It is not required to follow a specific form during the mentioned scanning, however, it is preferred that the data from the ground(l)surface scanned is collected to the extent possible. This minimizes the errors in the result.

During scanning; the signals from the detector(lO) search head(l l) related to the ground(l) and the position data from the optical tracking unit(20) with optical flow are received simultaneously. During scanning; the height changes between the ground(l) surface and the position tracking unit(20) are detected with the distance measuring sensor(23) and the correction of the position information is provided. During the scanning; the axial movements of the detector(lO) arising of the user’s hand and body movements are determined with at least one IMU sensor containing at least one gyroscope(24) and at least one accelerometer(25) and the correction of position information is provided. The signal and position data related to the ground(l) collected simultaneously and corrected as mentioned are transferred to the graphic processing unit(30) via cable or wireless communication unit(40). The ground(l) signal and position data transferred to the graphic processing unit(30) are converted into at least three dimensional series or matrix. The mentioned series or matrix; are subjected to interpolation and other graphic processing methods, missing data are completed and the probable noise is filtered.

The series or matrix containing the ground(l) signal and position data passing through the mentioned process are interpreted and displayed or mapped visually by the use of isometric curves and preferably color map are shown on the display(32). The mentioned map is interpreted and assessed by the user and accordingly, detections related to the cavities(2) under the ground(l) are performed.

The user can place some metal objects on the ground(l) to take place on the pay and constitute a reference, in order to specify the direction and positions before the scanning process.

Claims

1- The present invention is a metal detector or magnetic detector(lO) visualizing the underground(l) irregularities and cavities(2) for the user and it is characterized by containing;

A position tracking unit(20) integrated into or mounted to the detector(lO) structure in a manner to track the surface of the ground(l) scanned by the search head(l 1) of the mentioned detector(lO) by optical flow method, which provides the position data on the ground(l) scanned by utilizing the movement of the shades, in other words the patterns created by the geometric irregularities on the ground(l), in the image frame, or the sub-elements integrated into the detector(lO) body separately or in groups which perform the mentioned position tracking

At least one internal and/or external graphic processing unit(30) which provides the signals concerning the content of the ground/ 1) received from the detector/ 10) and position data received from the position tracking unit(20) to be converted into at least three dimensional signal-position data series or matrix and defines the mentioned series or matrix as isometric curves and/or color visuals and accordingly, displays these on an internal and/or external display(32) by visualizing and/or mapping; 2- It is the item in Claim 1 and it is characterized by; optimization of the operation frequency, search head/l l) geometry and signal processing system are optimized for detection of the ground/ 1) properties

3- It is the item in Claim 1 and it is characterized by; the placement of the position tracking unit(20) on the detector/ 10) shaft/ 12). 4 It is the item in Claim 1 and it is characterized by; containing an optical flow camera(21) and processor or integrated optical flow sensor within the position tracking unit(20), which provides sensing and tracking of the movement of the ground/ 1) patterns by optical flow. 5 It is the item in Claim 4 and it is characterized by; containing at least one no-contact distance measuring sensor(23) within the position tracking unit(20), which provides the continuous measuring of the distance of the optical flow camera(2l) to the ground(l).

6- It is the item in Claim 4 or 5 and it is characterized by; containing at least one IMU sensor with at least one gyroscope(24) or a structure formed by MEMS solutions for measuring the intertia

and/or

at least one accelerometer(25) or a structure formed by MEMS solutions for measuring the acceleration within the position tracking unit(20) which provides the detection of the axial movements of the detector(lO) originating from the user’s hand and body movements during scanning.

7 It is the item in Claim 4 and it is characterized by; containing lighting elements(26) within the structure of the position tracking unit(20) to illuminate the ground/ 1) so that the optical flow camera(2l) receives sufficient light

8- It is the item in Claim 7 and it is characterized by; automatic adjustment of the light intensity of the lighting elements(26) as based on the system requirements

9 It is the item in Claim 4 and it is characterized by; containing a cold mirror filter(27) within the structure of the position tracking unit(20), providing the prevention of reflections on the optical flow camera(2l) or integrated optical flow sensor.

10 It is the item in Claim 4 and it is characterized by; the lens(28) of the optical flow camera(2l), which has a moving structure.